Trees Hit Hard by Long-term Chronic Drought

May 31, 2013

LINCOLN, Neb. — While recent rains have helped spring growing conditions significantly, long-term chronic drought has caused significant decline in tree health across the state.

Nebraskans should pay particular attention to their trees and thoroughly water them if they begin to show sign of leaf droop or drying of foliage, especially at leaf edges, according to Eric Berg, Nebraska Forest Service community forestry program leader.

"Extended dry periods can result in tree decline or even death," Berg said. "Community tree inventories conducted over the last 30 years indicate a decline in the total number of trees across the state.  Severe weather, drought in particular, has caused severe and recent health declines and death, especially in many evergreen species."

Trees planted within the last 10 years are particularly at risk during prolonged and chronic drought conditions.

To check the soil moisture in the tree's root zone, push a long screwdriver or similar object into the soil.  If the soil moisture level is adequate, it should be fairly easy to push the screwdriver into the ground 8 to 10 inches, Berg said. If the ground is dry and in need of watering it typically is very difficult to push the screwdriver in beyond a couple inches. Supplemental watering should not be necessary if an inch or more of rain has fallen in the last week.

Deep, thorough watering will provide the most benefit to trees. Excessive watering should be avoided, especially in heavy soils with lots of clay, which may force air from the soil and cause roots to suffocate.  Care should also be taken not to water too much or too often as trees can as easily be killed from too much water as not enough.

"Infrequent deep watering – equivalent to 1-2 inches of rain – is the most beneficial to trees because it promotes healthier root systems, which are better able to sustain trees during times of drought," Berg said. "In contrast, frequent shallow watering tends to favor the growth of turfgrass."

Homeowners should keep in mind that root damage, soil compaction, wilt disease, insect infestations and over-watering can cause symptoms similar to those of stress from drought.

"This last year, below normal precipitation coupled with a very hot summer really took its toll on trees.  Beyond supplemental watering, homeowners can also take proactive steps to improve the health of their trees by maintaining a mulch ring 3-4 inches deep and several feet around each tree to help conserve soil moisture, eliminate competition from grass and reduce mower damage."

Fertilizing trees is not recommended if drought returns. 

"If the tree does not respond to watering it may be an indication that something else is wrong," Berg said. "In these cases a certified arborist should be contacted to help identify and manage the problem."

More information about locating a certified arborist can be found online (http://www.nearborists.org/search_for_arborist or http://www.isa-arbor.com/publicOutreach/findATreeCareService/index.aspx) or by contacting the Nebraska Forest Service at trees@unl.edu.